factory method a creational design pattern. factory method key features defines an interface for...
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Factory MethodA Creational Design Pattern
Factory MethodKey Features
Defines an interface for creating objects without needing to know each object’s type
Encapsulates the instantiation of concrete types
Leaves the details of instantiation to subclasses
Factory MethodUML
Factory MethodDocument Example
abstract class DocumentFactory {
public abstract Document getDocument();
}
class HTMLCreator extends DocumentFactory {
public Document getDocument() {
return new HTMLDocument();
}
}
class XMLCreator extends DocumentFactory {
public Document getDocument() {
return new XMLDocument();
}
}
abstract class Document {
...
}
class HTMLDocument extends Document {
...
}
class XMLDocument extends Document {
...
}
Factory MethodEncapsulation Example
class DocumentFactory {
public static Document getDocument(String file) {
int type = getType(file);
switch(type) {
case DocumentFactory.HTML:
return new HTMLDocument(file);
case DocumentFactory.XML:
return new XMLDocument(file);
...
}
}
Factory MethodBenefits
Types of created objects can be determined at runtime
Common interface allows for easier use by client classes
Useful for toolkits and frameworks
Limitations
Might need to subclass the factory to create concrete things (e.g., need to create an HTMLCreator to create an HTMLDocument)